Megaladapis, informally known as the koala lemur, is an extinct genus of lemurs belonging to the family Megaladapidae, consisting of three species that once inhabited the island of Madagascar. The largest measured between 1.3 to 1.5 m (4 to 5 ft) in length.
Description Megaladapis was quite different from any living lemur. Its body was squat and built like that of the modern koala. Its long arms, fingers, feet, and toes were specialized for grasping trees, and its legs were splayed for vertical climbing. The morphology of its foot suggests Megaladapis evolved to live in an arboreal environment, having a large hallux and lateral abductor musculature that helped it to grasp vertically on trees. These features are shared by other arboreal species. The hands and feet were curved and the ankles and wrists did not have the usual stability needed to travel on the ground that most other lemurids have. Its body weight reached 140 kg (310 lb). Other estimates suggest 46.5–85.1 kg (103–188 lb) but it is still much larger than any extant lemur. It had the largest body size of any lemur, with double the body mass of the next largest extinct lemur.
Cranial anatomy The shape of its skull was unique among all known primates, with a nasal region which showed similarities to those of rhinoceros, a feature that probably combined with an enlarged upper lip for grasping leaves. Its head was unlike that of any other primate; most strikingly, its eyes were on the sides of its skull, instead of forward on the skull as in all other primates. An endocast of its skull showed that it had a brain capacity of about 250 cc (8.8 imp fl oz; 8.5 US fl oz), about 3 to 4 times the size of a domestic cat's, which is small for its size when compared to other lemurs. Compared to the size of the skull, the diameter of the orbits protrudes outwards and forwards in a tabular form, suggesting that Megaladapis was diurnal. Details about the anterior parts of the dentition, such as the canines and incisors, are difficult to determine. The bulle osseve are broken away. The foremost facial portion and base of the skull is also wanting. The total length of the skull of M. madagascariensis has been calculated to be about 250 mm (9.8 in), about from three to four times that of a domestic cat. Based on the wear on the teeth, the obliteration of most of the sutures of the very thick bones, and the strongly developed crests, it is believed to have been an elderly individual. There are several well-preserved fragments of the upper and lower jaw. The premaxillae of Megaladapis projected anteriorly and were likely associated with a proboscis, while its palate was very elongated. Its long canine teeth and cow-like jaw formed a tapering snout. Its jaw muscles were powerful for chewing the tough native vegetation. Megaladapis had no permanent upper incisors and lacked an expanded articular facet on the posterior face of the mandibular condyle. This diet and similar phenotypic traits of the teeth are the basis for concluding a shared ancestry with the Lepilemur. The upper molars of Lepilemur are very close in shape to those of Megaladapis. The main difference between the two is that the outer crown-surface of Lepilemur's molars forms a nearly straight line, almost parallel with the long axis of the skull, and the outer side is slightly concave inwards. The antero-internal cingulum is missing in the molars of Lepilemur.
Biology
The island's topography was always changing, and like other lemurs, Megaladapis was specialized within its own niche. The general expectations of tree climbers such as Megaladapis is that with an increase in size, the body's forelimbs will also increase proportionally. The diet of Megaladapis might be the factor that influences the dental development; species with a larger brain, later initiation of molar crowns, and longer formation of crown are considered to have more of an omnivorous diet. In contrast, Megaladapis lived on a folivorous diet, despite having a smaller brain, early initiation of molar crowns, and fast crown formation. Based on the patterns of its dental microwear, M. edwardsi is believed to have been exclusively folivorous, being termed a "hyperfolivore". The other two species, M. madagascariensis and M. grandidieri, were also predominantly folivorous but had a more variable diet. Megaladapis fed using a leaf-cropping foraging method. Dental caries has been documented to have occurred in M. madagascariensis, which is a finding consistent with its folivorous diet that would have been highly cariogenic. Megaladapis were diurnal, or active during the day. Lemurs in general had small group sizes and were highly seasonal breeders (they breed for about one to two weeks a year), which is assumed to be the case for Megaladapis. Based on when molar crown initiation occurred, Megaladapis's gestation period is thought to have been at least 198 days, but was likely longer.
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